The invention relates to a method for operating a hybrid drive of a motor vehicle.
A hybrid drive of a motor vehicle is usually embodied as a parallel hybrid or power-split hybrid. The drive train of the motor vehicle usually has for this purpose an internal combustion engine and an electric machine. In a power-split hybrid, on the one hand the electric machine assists the internal combustion engine in driving the motor vehicle, and on the other hand, in a recuperation mode, the electric machine supplies an electric store and/or an electrical on-board power system of the motor vehicle with the necessary electrical energy.
In addition, in a hybrid drive the electric machine can be used to compensate a delayed response of the internal combustion engine in a transient mode by adjustment to a predefined torque value, i.e. the electric machine assists the internal combustion engine to reach a predefined torque value of the hybrid drive more quickly. Delayed response of the internal combustion engine occurs in turbo-charged diesel engines and, in particular, in turbo-charged petrol engines when so-called turbo lag occurs. In spark ignition engines, the delayed response and therefore a transient operating mode occurs as a result of the limited dynamics of the air path for the intake air. Spark ignition engines and diesel engines usually have an electronic throttle valve for regulating the air mass flow. The accelerator pedal is mechanically decoupled from this electronic throttle valve. The lag time of the intake manifold, the delayed charge air buildup of the turbocharger and dynamic charging effects in the air path do not permit highly dynamic setting of a predefined air mass flow and of the internal combustion engine torque which is generated as a result. Intervening in the ignition angle path allows the response behavior of the internal combustion engine to be improved, but in the process the efficiency of the internal combustion engine is degraded, as a result of which the fuel consumption and the exhaust gas emissions are increased.
The torque actuation of an electric machine has a much larger dynamic compared to internal combustion engines. For example, DE 10 2006 044 427 A1 describes a method for operating a hybrid drive of a motor vehicle in which a transient operating mode of the internal combustion engine is compensated by an electric machine. In this method, a dynamic drive train can be disadvantageously ensured only until the electric machine comes up against its system limits.